use a cloth measuring tape or a piece of leather lacing ,something that won't stretch to find circumference ,, lay the catchers mitt face down on a flat surface and measure the distance around,,30-32 inches is usually considered youth / little league size,,         33-36inches  teen/adult,,,,,,any measurement less than 30 inches inches is usually a childs or t-ball size,,if this info guide was of any value or assistance to you ,please vote below,,thanks zman5775